CHAPTER 12 - PATTERNS OF INHERITENCE = GENETICS
I. MENDELIAN GENETICS
A. PARTICULATE INHERITANCE
1. 2 particles/trait
2. 2 alleles/gene
B. PRINCIPLE OF SEGREGATION
1. Only 1 allele passed on/parent in gamete
2. Gamete = sperm in male; egg in female
3. Locus = site on chromosome where gene/allele found
C. PRINCIPLE OF INDEPENDENT ASSORTMENT
1. Alleles segregate randomly into gametes during meiosis
2. How 1 pair of alleles segregates has no effect on other alleles
II. SIMPLE MENDELIAN INHERITANCE (p. 223)
A. 1 GENE, 2 ALLELES
B. MONOHYBRID CROSS:
Gene = flower color Alleles: P = purple; p= white
Parent PP X pp è Pp Purple X White è All Purple
F1 (Filial) Pp X Pp Purple X Purple è Both!
F2 1PP + 2Pp + 1pp 3 Purple: 1 White
C. GENOTYPE - genetic make up; 1:2:1 (p. 225)
1. PP = Homozygous Dominant èDouble dose of dominant allele.
2. pp = Homozygous Recessive èDouble dose of recessive allele
3. Pp = Heterozygous èOne dose of each allele
D. PHENOTYPE - Physical appearance of a genotype; 3:1 (p. 224)
a. P_ = Purple (3)
b. pp = White (1)
E. PUNNET SQUARE - shortcut & organization (p. 226)
F. TEST CROSS - Cross unknown genotype with known Homo. recessive
(p. 231)
G. DIHYBRID CROSS (p. 229)
Where 2 genes are involved: Shape & Color
R = round, r = wrinkled, Y = yellow, y = green
P RRYY (round yellow peas) X rryy (wrinkled green peas)
F1 RrYy (round yellow peas) x RrYy (round yellow peas)
F2 first find the gamete possibilities = RY, Ry, rY, ry, for each
Genotypes - 9 Phenotypes - 4
RRYY 1 round yellow
RRYy 2 round yellow
RrYY 2 round yellow
RrYy 4 round yellow
RRyy 1 round green
Rryy 2 round green
rrYY 1 wrinkled yellow
rrYy 2 wrinkled yellow
rryy 1 wrinkled green
Total = 16 Phenotype Ratio= 9:3:3:1
III. EXTENSIONS TO MENDEL = GENETIC VARIATIONS
A. INTERMEDIATE/INCOMPLETE DOMINANCE (p. 234)
1. Neither allele dominates or masks other allele.
2. Blending: RR X R'R' = RR'
Red X white = pink
B. CODOMINANCE
1. Both alleles expressed, NOT blended.
2. R= red, Rw= white
RR X RwRw= RRw (red with white stripes)
C. MULTIPLE ALLELES (p. 234 - 235)
1. Expression of 1 trait/gene with more than 2 alleles
2. ABO blood types - 3 alleles
A & B codominant; O recessive
Phenotypes-4 Genotype(s)-6
A AA, AO
B BB, BO
AB AB
O OO
D. EPISTASIS - 1 gene regulates/affects another
1. Color in corn - 2 genes (A and B) (p. 236)
a. Need 1 dominant allele of each to be purple (dominant) color
b. If homo recessive for either allele è white
2. Labrador retrievers - 2 genes (E and B)
a. Need 1 dominant of E_ to be dominant color (Black or chocolate)
b. If ee è yellow lab
E. POLYGENIC - 1 trait controlled by 2 or more genes (p. 232 - 233)
1. Continuous variation
2. Height distribution
F. PLEIOTROPY = “many turnings” (p. 233)
1. 1 gene controls many traits
2. Sickle cell disease
G. ENVIRONMENT/EXPRESSIVITY (p. 235)
1. Arctic Fox, Siamese cat & Himalayan rabbit- warm areas pale, cool areas dark
2. Water buttercup
3. Primrose - red flowers < 300 C.; white flowers > 300 C.